1991 AES Annual Meeting Abstracts

MEXICO AS A CRITICAL FOCAL POINT FOR SHARK CONSERVATION.

With a known fauna approaching 100 species and with 40 of these of direct commercial importance, Mexico has the potential of having a sustained shark industry if strict conservation measures could be instituted. The basic problem is this country with two large oceanic shark faunas has yet to receive the biological studies that are necessary to locate the fishable stocks, to know seasonal populations, times and places where Mexican sharks have their young, and the migratory routes of the commercial species. Today the importance of sharks in the Mexican economy cannot be too strongly stated. Many poor mexicans practically subsist on a diet of shark meat. There is a vital need to sensitize the fishing secretariat concerning the problems and the positive effects of shark conservation. The most reasonable solution would be to train students to know and work within the shark industry or with the agencies of the government that would control this resource. One possibility is for interested foreign workers to plan joint research projects with Mexican investigators and students. The saving of the Mexican shark resource is a problem to which immediate attention is needed.

A PALEONTOLOGIST LOOKS AT THE MODERN LAMNIFORM SHARKS.

As a group the Lamniform sharks represent an order of neoselachian sharks known as far back as the Jurassic with an important middle Cretaceous radiation and another in the early Tertiary. It is the intention of this paper to suggest that the Lamniforms are richer and more varied than has been recognized in the past and the modern taxa, when considered with the fossil forms, show what is here termed the tip of the iceberg effect. Starting from a similar evolutionary base the primary direction in the food habits of these sharks has been the capture of fast moving organisms such as squid, fish, Cretaceous marine reptiles and mammals. This has resulted in a convergence of characters in the direction of fast, efficient predators which is reflected in overall body shape, fin size and shape, tooth structure and thermal heating. Two functional grades of these sharks can be recognized: a carcharoid grade of slow swimming fish feeders with complex needle-like teeth, and fast swimming lamnoids with flattened or more spike-like teeth. Lamna is an excellent example of the latter. Pseudocarcharias is a transitional form between these two groups. These groups have the value of functional levels and do not represent a taxonomic classification. The following 11 Recent families might be recognized: Paleocarcharridae, Carchariidae, Odontaspididae, Mitsukuriniidae, Megalochasmidae, Pseudocarchariidae, Alopiidae, Cetorhinidae, Carcharodontidae, Lamnidae and the Isuridae. The Anacoracidae or Squalicoracidae are not Lamniform sharks. The Alopiidae are set apart from the other lamniforms in retaining a primitive orectolobid character, that is, two gill slits over the pectoral fin. Contrary to some recent studies the lamniforms are almost certainly orectolobid derivatives.

REVIEW OF THE COMMERCIAL FISHERIES FOR SHARKS ON THE WEST COAST OF THE UNITED STATES.

Six species dominate commercial fisheries for sharks off the western U.S. The oldest, for soupfin shark (Galeorhinus zyopterus) [=galeus]) was decimated in 1944 but has continued to average between 150,000 and 250,000 lbs/yr. The largest (for spiny dogfish,Squalus acanthias) has been producing landings over 5 million lbs/yr. The blue shark (Prionace glauca) was experimentally fished between 1979 and 1980 and now is part of a longline fishery, with markets still being explored. A drift gill net and longline fishery for common thresher shark (Alopias vulpinus) and shortfin mako shark (Isurus oxyrinchus) has exhibited declining catches and size composition. This has required serious actions such as time/area closures, permit limitations, and low total allowable landings. Landings of Pacific angel sharks (Squatina californica) from a localized set gill net fishery peaked in 1985 and 1986 at 1.2 X 106 lbs/yr, but drastically fell due to decreased availability and alternative sources of low cost, imported shark meat. Landings of leopard shark (Triakis semifasciata) have fluctuated between 18,000 and 100,000 lbs/yr. The total west coast shark landings increased steadily through 1985, but have since declined and monitoring is needed to prevent stock depletion. Declines occur because slow growth, low fecundity and late age-at-maturity make sharks vulnerable to overfishing.

DEMOGRAPHY OF THE CENTRAL CALIFORNIA POPULATION OF LEOPARD SHARK (TRIAKIS SEMIFASCIATA).

Demographic analyses are useful in fishery management, but they require valid estimates of age-specific mortality and natality rates, as well as data on the distribution, abundance, habits and reproduction of the population. Such detailed demographic analyses have been completed for only three shark species: the spiny dogfish (Squalus acanthias), soupfin shark (Galeorhinus austrlis), and lemon shark (Negaprion brevirostris ). In California, reliable age-specific estimates growth, mortality, maturity, and fecundity are available only for the leopard shark, Triakis semifasciata. A demographic analysis of this species yielded a net reproductive rate (Ro) of 4.467, a generation time (G) of 22.35 yrs, and an estimate of the instantaneous population growth coefficient (r) of 0.067. If the present fishing pressure is included in the survivorship function, Ro and ‘r’ are reduced considerably, especially if leopard sharks first enter the fishery at early ages. A size limit of 120cm TL (estimated age of 13 yrs) for female sharks is proposed for the leopard shark fishery in central California.

NEW DATA ON THE REPRODUCTIVE BIOLOGY OF THE BUTTERFLY RAYGYMNURA ALTAVELA (LINNAEUS, 1758), (PISCES, GYMNURIDAE) FROM OFF THE TUNISIAN COASTS.

Distribution, sexual maturity, gestation, cyclic vitellogenesis and fecundity of butterfly rayGymnura altavela (Linnaeus, 1758) from off the tunisian coasts are described. Size at first sexual maturity of males is reached after 78 cm of disk width (DW). Females keep juvenile apparatus until they reach 67 cm DW; thereafter maturation proceeds between 68 and 102 cm DW. The first adult females are 102 cm DW. Females are larger than males. Gestation takes place during six months or more. Vitellogenesis starts against at mid gestation; it is a semi-delayed vitellogenesis as in some squatinidae. There is probably one reproductive cycle per year.

MOVEMENTS OF PELAGIC SHARKS.

Blue sharks, Prionace glauca, swim slowly, usually at speeds of less than 1 knot (52 cm/sec). Comparison of swimming speeds from telemetry with speed of travel from tag returns suggests that the sharks make use of favorable ocean currents in their movements. Telemetry experiments in the Gulf Stream and eddys south of New England appear to show instances of such use of currents. While 1 knot seems a low speed for such a large fish, the sharks swim continuously and, on a time scale of seasons, can easily cross ocean basins. Such migrations seem to be a normal activity for Prionace allowing it to include widely separated areas for purposes of feeding, breeding, and reproduction in a fashion which is still poorly understood. These migrations also make the sharks vulnerable to the longline fisheries of many nations and will complicate their management.

THE BIOLOGY OF THE FINETOOTH SHARK (CARCHARHINUS ISODON).

The finetooth shark (Carcharhinus isodon) appears in the nursery and mating areas of South Carolina when the surface water temperature rises above 20°C in May. Both adults and juveniles are common in shallow coastal waters through the summer. It migrates southward as the surface water temperature decreases below 20°C in the fall. It winters off southern Florida. The finetooth shark has consecutive, year-long ovarian and gestation cycles. Mating females carry 9-11 oocytes about 30mm in diameter. During mating, the male deposits a large spermozeugma into each uterus. The embryos develop a placental connection. Females carrying young 480-550mm TL enter the nurseries after the northward migration in late May. Parturition occurs from late May to mid-June, after a gestation period of about twelve months. The young measure 480-561mm TL at birth. After parturition females start developing the next batch of oocytes which will be ovulated the following May.

HISTOLOGICAL OBSERVATION ON REPRODUCTIVE SYSTEM OF BLACKTIP SAWTAIL CATSHARK, GALEUS SAUTERI.

Morphology and histology of reproductive organs of blacktip sawtail catshark, Galeus sauteri, were studied from 150 specimens caught in northwestern Taiwan waters. (1) The seminiferous part of the testes shows a zonate and follicular structure supported by interstitial cells. Three zones are distinguishable: zones of tubulogenesis, tubules with different stages of spermatogenesis, and tubules containing spermatozoa or interstitial cells. The epididymis ductus deferens and seminal vesicle with spermatozoa were also observed. (2) The reproductive cells which appeared in the epithelial cells of the ovary sink into the ovarian cortex where they were covered with a simple epithelium of follicular cells to become an oocyte. The developed oocyte is filled with the yolk globule. Although many oocytes appeared in the ovary, mature oocytes that failed to be ovulated degenerated and were absorbed during the course of development. (3) The process of formation of the egg case in the shell gland of this species is similar to other oviparous sharks. Two egg cases were formed during gestation. (4) The proximal portion of the pelvic fin of male sharks are modified into an elongated copulatory organ known as a clasper. The skeleton of the pelvic fin and clasper consisted of basal cartilages, the metapterygium and propterygium radial cartilages and ceratotrichia, joint cartilage, beta cartilage, and main stem cartilage. The terminal cartilages include the claw, rhipidion, ventral terminal cartilage and spur.

MAGNETIC RESONANCE IMAGING OF THE ELASMOBRANCH CHONDOCRANIUM.

Magnetic resonance imaging is a relatively new medical imaging procedure which can demonstrate subtle differences in adjacent tissues. The technique was employed to examine the chondocrania of several species of elasmobranchs including Squalus sp., Carcharhinussp., and Dasyatis sp. In addition to revealing cranial anatomy in sagittal, coronal, and axial planes, a ferromagnetic disturbance was detected in the region of the sacculus and endolymphatic ducts of all four Squalus specimens. Several samples of ferromagnetic material were tested to reproduce and quantify the disturbance found in the dogfish chondocrania.

HOMING AND SITE ATTACHMENT OF JUVENILE LEMON SHARKS,NEGAPRION BREVIROSTRIS: A PRELIMINARY REPORT.

Prior behavioral studies on juvenile lemon sharks using ultrasonic tracking have indicated that the juvenile sharks have a restricted activity space but did not indicate long term site attachment. To determine the degree of site attachment over time, we have conducted periodic censuses of particular sites in the North Sound at Bimini, Bahamas over a period of 8 months. Of 45 recaptured sharks, 36 were recaptured at the same site as originally captured, 6 were recaptured at adjacent sites, and only 3 were recaptured at distant sites. To determine the sharks’ ability to return to its activity space, Age 0 sharks were implanted with ultrasonic transmitters, tracked to determine their activity space, and then removed to one of 3 predetermined sites 4 km away and released. After translocation, 4 out of 4 sharks returned to their activity space within 12 hours of release. Two sharks were translocated to a second site. One returned to its original activity space while the other one went elsewhere and established a new activity space. These preliminary findings indicate a high degree of site attachment and an ability to return to their activity space when displaced from it. The continuing study will focus on sensory mechanisms and orientation strategies for homing in juvenile lemon sharks. Supported by NSF – OCE 8843425.

ANATOMY OF RHINOCHIMAERA PACIFICA (HOLOCEPHALI: RHINOCHIMAERIDAE).

All three genera of long-nosed chimaeras are grouped into a single family based on the presence of a long snout; however, when other characters are considered, Rhinochimaerastands apart from Harriotta on the basis of skeletal characters such as tooth plate morphology and cranial shape. I have dissected and skeletonized Rhinochimaera pacificaand Harriotta raleighana to examine head morphology of long-nosed chimaeras. Outgroup comparisons were made to Callorhinchus milii, Hydrolagus colliei, H. novaezelandiaenbsp;and Chimaera sp. Rhinochimaera superficially resembles Harriotta, but when subjected to detailed comparative analysis it appears that Harriotta more closely resemble chimaerids than it does Rhinochimaera. The evolution of a hyoid arch muscle inserting into connective tissue of the snout is a synapomorphy of chimaeroids. This is the first detailed musculo-skeletal description of any rhinochimaerid.

PROTECTIVE NETTING AND SHARK CONSERVATION.

Natal’s protective shark nets are thought to act primarily as a fishing device; by reducing numbers of large sharks the likelihood of a shark/bather encounter is similarly reduced. The nets may also have a secondary function as a physical deterrent, although they do not form an impenetrable barrier. The netting operation constitutes, in effect, a multi-species shark fishery, yet there have been few attempts to assess it as such. Is it possible to assess the effect of almost thirty years of netting on local stocks? Are the dual aims of bather protection and shark conservation compatible? Can sustainable catches for each species of shark be determined and fishing effort regulated accordingly, but without prejudicing bather safety? These questions are being addressed and methods of stock assessment sought.

ELASMOBRANCH CONSERVATION ON AN INTERNATIONAL LEVEL: ESTABLISHING AN SSC SHARK SPECIALIST GROUP.

The Species Survival Commission of the World Conservation Union (Switzerland) has authorized the establishment of a Shark Specialist Group. The mission of this group will be to serve as a focal point for international efforts on conservation of elasmobranch fishes. One of its main goals will be the publication of a Shark Action Plan. This plan will specify research and conservation priorities, and will be used to direct these activities on a regional and international basis. The first activity of the group will be to form a panel of motivated specialists. Major issues to be considered will be : 1) misapplication of fishery models and techniques 2) wasteful harvests of shark parts 3) uncontrolled impact of drifting nets and long lines 4) vulnerability of mating aggregates and juveniles. Supported by IUCN/SSC.

MECHANICS OF FLAPPING RAY LOCOMOTION

Rays exhibit one of two basic patterns of movement during locomotion, an undulation of the distal edge of the fin, or a large amplitude flapping motion. Two species in the family Myliobatididae, the cownose ray, Rhinoptera bonasus, and the bullnose ray, Myliobatis freminvilei, swim using the large amplitude flapping motion. Individuals from these species were filmed swimming in a recirculating flow tank at the Duke University Marine Laboratory. The animals’ movements were quantified and a mathematical description of the motion was developed. Lift and drag coefficients for a series of fin elements were measured using casts of rays in a wind tunnel. The kinematics of these rays are unique in that their fins oscillate, at approximately 1 Hz, perpendicular to the direction of the animals’ propagation twisting less than 25 degrees from that direction. The advance ratio (J=V/nd), calculated using the maximum tip speed, is unusually high with a minimum value of 4, indicating that rays are not using a typical propeller like mechanism for generating thrust. A hypothesis for the mechanics of thrust generation has been developed and a quasi-steady model of the forces acting on the ray produced.

CONSERVATION AND MANAGEMENT OF THE WESTERN NORTH ATLANTIC SHARK RESOURCE BASED ON THE LIFE HISTORY STRATEGY LIMITATIONS OF SANDBAR SHARKS.

The life history strategy of sharks is very different from most boney fish and appears to fall in the ralm of “K selected species” of classica r/K selection theory. The intrinsic rate of increase (r) for sandbar sharks was estimated from a life history model, in order to define recruitment overfishing. Incorporating the best potential biological estimates yields an r of 10%. Thus, fishing mortality of around 5% may be sustainable. Reported commercial landings grew 8 fold in the last 5 years. On average, for the past 10 years, motality exceeded MSY estimates by 40%. Yield from a fishery is directly related to the r and the effort applied, thus a low r value has significant effect on the sustainable effort level. Modeling costs, revenues and profits illustrates that the open access fisher will be inefficient, with too much effort, low yield, and low biomass. Management resources are proposed.

CALIFORNIA’S PELAGIC SHARK FISHERIES.

California’s highly successful drift gill net (DGN) fishery and the experimental drift longline fishery both focus on the pelagic species of common thresher, shortfin mako and the blue sharks. The DGN fishery for thresher sharks developed off the southern California coast in the late 1970’s and was decimated by 1989. Management was influenced by special interest groups more concerned with their own interests than shark resources. Shortfin mako sharks were an incidental but valuable by-catch in the DGN fishery. Catch and effort closely followed that of the DGN fishery until 1989 when California opened an experimental longline fishery for shortfin mako and blue sharks. In an effort to minimize wastage, the experimental fishery attempts to utilize the local blue shark resource through a mandated market development program.

SPORTFISHING TOURNAMENTS FOR SHARKS IN FLORIDA, 1975-1990.

The number and size of recreational shark tournaments in Florida increased from the mid-1970’s into the latter 1980’s, then began to decline. At least 31 separate shark tournaments were conducted at different sites in Florida waters on a regular basis during the 1980’s. Catch data from these tournaments indicate recent downward trends in catch per unit effort, total sharks entered, largest sharks entered, and average shark weight. Since 1988, many Florida tournaments have experienced difficulties due to several factors, primarily the lack of large sharks and the rising conservation movement. “Kill” tournaments are yielding to conservation pressure to incorporate limited-kill or no-kill options. A 100% catch-and-release format, the Gulf Coast Shark Census, has been developed as a timely alternative to the traditional kill format.

POPULATION TRENDS OF ELASMOBRANCH SPECIES WITHIN A CENTRAL CALIFORNIA ESTUARY OVER A FORTY YEAR PERIOD, AS DETERMINED FROM SPORT DERBY DATA

Date from 48 central California elasmobranch sport fishing derbies were collected and analyzed for shifts in population dynamics. The derbies were all held in Elkhorn Slough (Monterey Bay) from 1951 until 1990 under similar data collection regimes. For each derby, the catch composition and (when effort was known) CPUE were analyzed. The three most abundant species in the catch, bat rays (Myliobatis californica), shovelnose guitarfish (Rhinobatos productus) and leopard sharks (Triakis semifasciata), were also analyzed for length-weight relationships, sex ratios and trends in size class distributions. The data show several shifts in the catch composition over the last 40 years, including the relative disappearance of shovelnose guitarfish from the later catches. While the CPUE data are scanty, a CPUE peak during the mid to late fifties is evident. The bat rays and shovelnose guitarfish both exhibit a female to male sex ratio of 2:1, while Leopard sharks maintain a 1:1 sex ratio. No apparent size class shifts can be discerned from the bat ray or leopard shark data. However, smaller size classes of shovelnose guitarfish disappear from the catch before the decade of the seventies.

THE IN SITU FEEDING BEHAVIOR AND ASSOCIATED ELECTRIC ORGAN DISCHARGE OF THE PACIFIC ELECTRIC RAY, TORPEDO CALIFORNICA

Pacific electric rays ambush their fish prey from the bottom during the day and actively search for prey while swimming in the water column at night. Predatory motor patterns and electric organ discharges (EODs) were recorded on video and audio channels of a housed 8mm camcorder. Rays were presented four prey stimuli: life (LF); freshly-killed (FKF); frozen fish (FF); and a simulated bioelectic field (EF), to which rays responded with different EOD characteristics. Day/night predatory motor patterns were of four phases: 1) jump (simultaneous with EOD initiation); 2) pectoral-fin cupping; 3) orientation; and 4) ingestion. Rays responded to “LF” with the highest initial pulse rates, while “FKF” received the longest pulse trains. Attack latency was longest for “EF” and shortest for “FF.” Pulse rates may vary on pre-attack assessment of prey health state rather than being fixed at the beginning of the attack. Pulse train lengths and other EOD characteristics may vary depending on feedback from prey during an attack.

A POLITICAL PROSPECTIVE OF SHARK CONSERVATION IN MEXICO

Legally shark fishing in Mexico is controlled by the government which in many cases consists of persons that have little knowledge of sharks or shark fishing. Statistically sharks are not treated as separate species but divided into two categories: tiburones, those sharks over 1 meter, and cazones, or sharks around a meter or less. Often the same species is treated in this manner. There have been few sustained shark fisheries in Mexico. The oldest is that of Mazatian for many years and also near Alvarado Veracruz. Recent failures have occurred in Baja California Sur, Tecouluta Varacruz and in Chiapas. A fishery exists in Quintana Roo that has shown with varying amounts of success. Usually much of the shark resource is wasted in that only the meat is used, or at other times, just the fins or the skin. We know of only one instance where an attempt was made to utilize the whole shark. In 1976 a group concerned with studying Mexican sharks was formed at the University of Mexico. This group has taken the name Cipactli which is the nahuatl name for sharks. Their work resulted in the publication of a Mexican book on sharks called Tiburones Mexicanos.

A PRELIMINARY REPORT ON THE RATE OF NATURAL MORTALITY OF JUVENILE LEMON SHARKS, NEGAPRION BREVIROSTRIS

Determination of teh natural mortality is an important step in understanding and quantifying the population dynamics of a species. This study, the first of its kind in sharks, was begun in the Florida Keys, but when our CPUE dropped an order of magnitude from 0.384 lemon sharks per gill net hour in 1988 to 0.049 lemon sharks per gill net hour in 1989, we were forced to move the study to Bimini, Bahamas. The population of juvenile lemon sharks in the Bimini study area suffers virtually no fishing mortality and natural mortality is being determined using a multiple census technique. Early results of the study indicate natural (total) mortality to be extremely high (Z=1.5) during the summer of first year (Age 0). This mortality rate drops dramatically in the summer of the second (Age 1) and third years (Age 2). The importance of these early findings are discussed with relation to population dynamics and shark conservation. Supported by NSF – OCE 8843425.

GENETICS OF SHARK POPULATIONS: WHERE ARE WE AND WHAT CAN WE HOPE TO KNOW

Effective management and conservation of exploited or threatened species requires knowledge of the population structure of the species. This can be obtained by direct methods, like mark-recapture, or by indirect genetic analysis of populations. In this seminar I will review the available techniques of genetic analysis and their applications for understanding the population biology of sharks.

A PHYSIOLOGICAL MOLECULAR CLOCK FOR MITOCHONDRIAL DNA: EVIDENCE FROM SHARKS AND MAMMALS.

It is generally believed that mitochondrial DNA (mtDNA) in vertebrates evolves at a lineage-independent rate of about 0.5-1.0% per million years. We tested the generality of the molecular clock hypothesis for mtDNA by estimating the rate of mtDNA evolution for an ancient group of vertebrates, the sharks. Our analysis takes advantage of the superlative fossil record for 2 distinct orders of sharks to provide robust estimates of substitution rates, which we show to be lower than those for primates. Based on these data and re-analysis of published data from mammals, we propose a general theory of mtDNA evolution that strongly implicates oxygen metabolism as the primary determinant of variation in substitution rates of mtDNA among taxa.

THE ROLE OF PUBLIC EDUCATION IN ELASMOBRANCH CONSERVATION.

The Monterey Bay Aquarium opened its temporary (one-year) Sharks exhibit in January of 1991, featuring live sharks and a series of interactive exhibits. The exhibit was augmented by theater presentations, lecture series, family workshops, an art festival, high school and public auditorium programs and publication of a natural history book. The primary educational goal of the exhibit and supporting programs was to debunk the popular “Jaws” image while increasing the public’s interest in elasmobranch conservation. Approximately 1.7 million people will have visited the Sharks exhibition and 10,500 participated in specific education programs. Visitor experience and effectiveness of the exhibit were formally evaluated using pre- and post-visit interviews. This paper describes the exhibit, presents evaluation results and discusses the role of scientists and the media in conservation education.

STATUS AND REVIEW OF THE CALIFORNIA SKATE FISHERY.

Since 1916, the annual commercial catch of skates and rays in California has ranged from 26 MT to 347 MT. Nintey-five percent of the catch is taken by drag boats in northern and central California. While 20 species of rays and skates have provisionally been recorded from California waters, 3 species (Raja binoculata, R. inornata and R. rhina occur consistently and dominate the commercial landings and 1 species, Myliobatis californica, the sport landings. The utilization and seasonality of the commercial catch and the biology of the dominant species are discussed.

HOME RANGE, DIEL ACTIVITY RHYTHMS, AND HABITAT SELECTION OF JUVENILE LEMON SHARKS, NEGAPRION BREVIROSTRIS (POEY).

Ultrasonic transmitters were surgically implanted into the coeloms of 38 lemon sharks, yielding 2281 telemetry fixes. Activity space area averaged 0.88 km2 (range = 0.23-1.26 km2) and was positively correlated with shark size. Indices of site attachment and defense reveal that juvenile lemon sharks establish an undefended home range. Rates of movement (median= 0.21 body lengths per second, range = 0-1.46 bl/s) revealed orepuscular peaks in diel activity. Water depth, temperature and bottom type were used disproportionately to their availability. Specifically, juvenile lemon sharks selected shallow, warmer water with an underlying rocky or sandy substrate, perhaps as a means of predator avoidance.

ANALYSIS OF SHARK CATCHES FOR 1974-1990 FOR THE CHESAPEAKE BIGHT REGION OF THE U.S. MID-ATLANTIC COAST.

Recent assessments indicate that the shark stock of the Western North Atlantic is exploited at a rate twice the maximum-sustainable-yield. This finding is supported by data generated by the VIMS longline program for sharks of the Chesapeake Bay and adjacent coastal waters. Trends in catch-per-unit-effort since 1974 indicate as much as five fold reductions in population size for the common species. Declines include numbers of individuals for all species, all size classes within species, and in one case a strong decline in relative abundance. Results suggest that continued unregulated exploitation will cause a total stock collapse for which recovery will require decades. Such a biological disaster would also have negative socio-economic impacts on user groups associated with this marine resource.

AN ACOUSTIC TRACKING OF A MEGAMOUTH SHARK, MEGACHASMA PELAGIOS.

A 4.9 m shark (the 5th known specimen) was captured Oct. 21, 1990 in a drift gill net, towed 13 km to Dana Pt. Harbor, and restrained by tail rope overnight. The next afternoon it was towed to sea and released with two attached ultrasonic transmitters (one with depth sensor). It was tracked for 50.5 hours, during which it made distinct vertical moves at each dawn and dusk transition, staying shallow at night (11-22 m depth range) and deeper during the days (120-166 m, well above the 700-850 m bottom). These moves appeared triggered by light changes. Horizontally, the shark moved slowly (0.95 km/h rate), on a relatively straight path, with no clear diel changes. Previously proposed feeding patterns are considered re: these findings.

THE PRICKLY SHARK ECHINORHINUS COOKEI, COLLECTION, AND DISPLAY OF THIS RARE DEEP-WATER SHARK.

The prickly shark, Echinorhinus cookei, found at depths of up to 1,000 meters was collected by the staff of the Monterey Bay Aquarium at the head of the Monterey submarine canyon near Moss Landing. This bottom-dweller is recorded from the coast of Monterey south to Baja California, and in the waters adjacent to Peru, Hawaii, New Zealand, Taiwan and Japan. This sluggish animal feeds on fishes, other sharks, octopus, squid and crustaceans. Using S.C.U.B.A., divers collected a single specimen at 33 meters depth. This specimen was transported to M.B.A. and displayed for seven days. During this time problems arose that affected buoyancy. It is hypothesized that this may be due to the large liver of this species. After seven days the shark was returned to the ocean. Future research is being planned to understand the problems in displaying deep-water elasmobranchs.

OBSERVATIONS ON THE DIRECTED AND BYCATCH LONGLINE FISHERIES FOR SHARKS IN THE NORTHERN GULF OF MEXICO.

A market for shark products developed concurrently with the development of a domestic tuna fishery in the Gulf of Mexico, so a directed, as well as a bycatch, longline fishery for sharks became established around 1986. Shark landings soared from 1.9 mil lb in 1986 to 12.4 mil lb in 1989. Observers recorded catch composition and effort data from 53 shark sets and 190 tuna sets between 10/89 and 9/90. The shark sets produced 1,180 shark which were retained for sale and 268 sharks which were discarded (21 alive). Predominant species were blacktip sharks, smooth dogfish, and Atlantic sharpnose sharks. Catch rate for shark sets was 8.3 sharks/100 hooks. Shark bycatch from the tuna sets consisted of 75 sharks retained for sale and 281 discarded (195 alive). Predominant species were spinner, blacktip, dusky, sandbar, and scalloped hammerhead sharks. Catch rate on tuna sets was 0.4 sharks/100 hooks. Sex ratios and total lengths were also recorded.

OBSERVATIONS ON THE REPRODUCTIVE BIOLOGY OF BAMBOO SHARKS (HEMISCYLLIDAE) MAINTAINED IN CAPTIVITY.

In 1985, Sea World of Florida initiated a captive breeding program consisting of three species of orectolobiform sharks: epaulette shark, Hemiscyllium ocellatum; brownbanded bambooshark, Chiloscyllium punctatum; and whitespotted bamboo shark, C. plagiosum. Mating behaviors have been observed in all three species. Two species, Hemiscyllium ocellatum and Chiloscyllium punctatum have produced numerous offspring. Gestation period at 24°C was 138da for H. ocellatum, and 160da for C. punctatum. Size at birth ofH. ocellatum was 133mm TL, size at birth for C. punctatum was 158mm TL. Temperature affects gestation time; a temperature increase of 3°C decreases gestation period by 14% in H. ocellatum, and by 27% in C. punctatum. After 12 to 16 mo, mean TL for H. ocellatum was 418mm, mean TL for C. punctatum was 450mm.

A POLITICAL PROSPECTIVE OF SHARK CONSERVATION IN MEXICO.

Legally shark fishing in Mexico is controlled by the government which in many cases consists of persons that have little knowledge of sharks or shark fishing. Statistically sharks are not treated as separate species but divided into two categories: tiburones, those sharks over 1 meter, and cazones, or sharks around a meter or less. Often the same species is treated in this manner. There have been few sustained shark fisheries in Mexico. The oldest is that of Mazatlan for many years and also near Alvarado Veracruz. Recent failures have occurred in Baja California Sur, Tecouluta Veracruz and in Chiapas. A fishery exists in Quintana Roo that has shown with varying amounts of success. Usually much of the shark resource is wasted in that only the meat is used, or at other times, just the fins or the skin. We know of only one instance where an attempt was made to utilize the whole shark. In 1976 a group concerned with studying Mexican sharks was formed at the University of Mexico. This group has taken the name Cipactli which is the nahuatl name for sharks. Their work resulted in the publication of a Mexican book on sharks called Tiburones Mexicanos.

GROWTH RATES AND AGE ESTIMATION OF SEVENGILL SHARKS,NOTORYNCHUS CEPEDIANUS AT THE MONTEREY BAY AQUARIUM.

Growth was measured on 5 juvenile sevengills and von Bertalanffy growth curves were fitted to the data using Fabens’ method. The von Bertalanffy growth model was inadequate in fitting the whole range. Therefore, an alternative method of growth analysis based on the von Bertalanffy model was used for the upper end of the range. Age of the five juvenile sevengills was estimated from calculations based on the von Bertalanffy model using the growth curve for each individual shark. The results confirmed the original age estimates that 2 of the sharks were approximately 5 months old when collected and 3 of the juveniles were 18 months old when collected. Length/age data were then used in an exponential regression based on the von Bertalanffy model. Age at sexual maturity for males and females was estimated to be 4 to 5 yr and 16 to 24, respectively.

BUOYANCY OF DEEP-SEA SHARKS.

Buoyancy of 7 species of deep-water squalids and 1 scyliorhinid shark collected in New Zealand waters was determined by measuring their weights in air, weight in water, and volume. Liver density and the area of surfaces capable of providing hydrodynamic lift were also measured. All species of deep-water sharks were neutrally buoyant or nearly so; weights in sea water were -3.5 to +2.0% of their body weights in air. There was considerable variation between species, but buoyancy was relatively constant for different size individuals within species. Size of fins and tail were not correlated with buoyancy, and these hydrodynamic features appear to be relatively unimportant for buoyancy. Liver size was fairly constant within species, accounting for about 20% of body weight. Buoyancy characteristics of the scyliorhinid shark were similar to those of shallow-water sharks, and differed from those of the deep-water squalid sharks. Despite minor variations in features that contribute to increased buoyancy, deep-water sharks of different species and sizes all maintained densities similar to the surrounding water.